The number of drugs supplied in lyophilized or powdered form has been growing at an increased rate over the past several years, reflecting the increase in the introduction of biological drugs. For example, because of stability and shelf life factors, therapeutic proteins are often formulated as powders that must be reconstituted prior to injection. A growing number of drugs and biologics supplied in powder form are including reconstitution vial systems that incorporate a vial adapter or vial transfer device. Dual chamber drug cartridges and syringes go a step further and allow reconstitution to take place within the device immediately prior to injection. This allows, for example, a diluent to be added to a dehydrated, lyophilized, desiccated or powdered active substance immediately prior to injection, which is particularly useful for substances that are subject to degradation or loss of activity when stored in a liquid form.
The majority of mixing devices for syringes utilize sequential chambers, wherein the syringe has one barrel having a proximal chamber and a distal chamber separated by, for example, a membrane or elastomeric seal. A number of such sequential-chamber mixing syringes utilize a bypass protrusion at a section of the barrel to enable fluid in the proximal chamber to bypass the dividing membrane and mix with the fluid or powder in the distal chamber.
Some other mixing syringes utilize concentric barrel configurations. Many concentric barrel mixing syringes to date, however, require complex assemblies, multiple operation steps by the user, or other particular nuances that make them difficult to manufacture, assemble, or operate. For example, some existing concentric barrel mixing syringes require concentric inner and outer barrels that are selectively rotatable with respect to each other, and require one or more sealing rings that contain a passage means therein. The barrels must be rotated to align a hole in the inner barrel with the passage means in a sealing ring. Such configurations require complex components and cumbersome requirements for the user to operate the device. Other concentric barrel designs utilize outer and inner telescopic tubular elements seated inside a barrel and coaxial with the longitudinal axis. The outer tubular element and barrel form a chamber which holds a reservoir of liquid. The inner tubular element has an end nearby the injection port with a seal thereon that has an orifice therein. Accordingly, such mixing syringe configurations require three tubular elements, with the outer and inner concentric chambers residing inside a third barrel. Still other dual chambered syringes have concentric inner and outer barrels that form an annular space to hold a fluid and utilize one or more apertures between the inner and outer barrels to enable flow of a liquid from the annular space into the inner barrel and thereby mix the liquid with a substance in the inner barrel. As with other mixing devices comprising concentric barrels, these are also complicated in structure and often require rotation of the barrels to align one or more apertures that enable a flow of a liquid substance from one chamber into another.
Thus, there are complexities associated with the use of concentric barrels for mixing syringe configurations. In addition to those described above, mixing syringes utilizing concentric barrels must also address factors such as maintenance of container sterility, interaction of components for sealing, venting requirements, and distribution of internal forces, among other factors. As such, various sterility, sealing and venting arrangements have been used which have limitations in terms of ease of manufacture and operation of the mixing device. Given the complexities of current drug substances, particularly related to sensitive biologics, there remains a need for mixing syringes that provide ease in manufacture, maintenance, and handling.